Controlled Synthesis Of Atomically Dispersed Noble Metal Catalysts And Their Electrocatalytic Applications

Noble metal nanomaterials exhibit excellent catalytic property in many fields such as industrial catalysis and energy conversion,and have received increasing attention and research.In terms of the field of effective development and utilization of hydrogen energy,the precious metal platinum has been recognized as the most ideal electrocatalyst for hydrogen evolution reduction due to its moderate hydrogen adsorption free energy.Improving the atomic utilization efficiency of precious metals has always been a focused and important topic.The catalytic properties of noble metal catalysts can be significantly affected and optimized by their surface atomic arrangement and electronic structure.In recent years,with the continuous advancement of nano-synthesis technology and characterization methods,more and more researchers are committed to regulating precisely the surface atomic structure and coordination environment of noble metal catalysts to optimize their catalytic activity,such as regulating the size of nanoparticles,constructing core-shell structure with the shell of the active metal component or alloys,adjusting crystal planes and crystal phases,etc.In particular,the controllable synthesis of noble metal catalysts with atomic precision can not only continue the high activity and stability of noble metals,but also ensure their high atomic utilization efficiency,which significantly promoting the efficient utilization of noble metals to a new level.In this dissertation,we focused on the precise design and preparation for various energy-related noble metal catalysts with atomic dispersion towards electrocatalytic hydrogen evolution reaction(HER)and oxygen reduction reaction(ORR).Through precise regulation of the surface atomic structure of noble metal catalysts,we can effectively economize noble metals and further optimize their electrocatalytic activity.Moreover,the fine structures and structure-activity relationships of noble metal nanocatalysts can be deeply explored with the help of advanced characterization methods and theoretical calculations.The primary contents of the dissertation are listed as follows:1.We summarized recent progress about the synthetic strategies,characterization methods and electrocatalytic applications of atomically dispersed noble metal catalysts.We then introduced the research significance and main contents.2.The atomically dispersed Cu on ultrathin Pd nanoring was prepared via the underpotential deposition method and thermodynamic control,and then were used as seeds to synthesize atomically dispersed Cu-Pt dual site alloyed with Pd nanoring.Spherical aberration corrected high-resolution transmission electron microscopy and Xray absorption fine structure(XAFS)characterization confirmed that Cu and Pt species are both atomically dispersed,and Cu and Pt atoms were coordinated to form Cu-Pt dual site structure.The trimetallic single atom alloy catalyst exhibited superior HER activity under acidic conditions.Theoretical calculations indicated that single Pt atom is the active site for HER and the adsorption free energy of hydrogen is moderate.In addition,the adjacent Cu atom is necessary to balance the interaction between hydrogen atoms and single Pt atoms,thereby effectively promoting the electrocatalytic activity of Pd/Cu-Pt nanoring.3.Using the Pd/Au screw-like nanowires as seeds,atomically dispersed Pt alloyed with Pd/Au screw-like nanowire was prepared.The fine structure of atomically dispersed Pt was demonstrated by aberration-corrected high-resolution transmission electron microscopy and XAFS techniques.The electrocatalyst with highly dispersed Pt atoms and abundant surface defects possessed remarkable electrocatalytic activity for acidic hydrogen evolution reaction and alkaline oxygen reduction reaction.4.In proton exchange membrane fuel cells,the cathode ORR possess a rather slow kinetics and require much higher Pt content about 3-5 times than hydrogen oxidation reaction,which severely restricts the large-scale application of fuel cells.Therefore,the precise design of effective Pt-based electrocatalysts has attracted extensive attention and research.The doping of other elements has been reported as an effective strategy to influence the catalytic performance through ligand and strain effects.Hydrogen atom with the smallest atomic radius,can easily enter the interstitial site of noble metal to change the lattice constant and electronic structure,thereby optimizing catalytic activity and selectivity.We have introduced hydrogen atom into PtPd nanotube to adjust its atomic and electronic structure.Theoretical calculations indicated that the catalyst with optimized structure possessed appropriate binding ability between Pt and reaction intermediates,thereby substantially promoting ORR catalytic activity and stability.